Peridynamic modeling of thermo-oxidative damage evolution in a composite lamina

Surface oxidation degrades the durability of polymer marix composites operating at high temperatures due to the presence of strong coupling between the thermal oxidation and structural damage evolution. The mechanism of oxidation in polymer matrix composites leads to shrinkage and damage growth. The thermo-oxidative behavior of composites introduces changes in diffusion behavior and mechanical response of the material. This study presents the derivation of peridynamic formulation for the thermo-oxidative behavior of the polymer matrix composites. As a demonstration purposes, isothermal aging of a unidirectional composite lamina is presented by using peridynamics. Oxidation contributed to the damage growth and its propagation

Peridynamics for bending of beams and plates with transverse shear deformation

Progressive failure analysis of structures is still a major challenge. There exist various predictive techniques to tackle this challenge by using both classical (local) and nonlocal theories. Peridynamic (PD) theory (nonlocal) is very suitable for this challenge, but computationally costly with respect to the finite element method. When analyzing complex structures, it is necessary to utilize structural idealizations to make the computations feasible. Therefore, this study presents the PD equations of motions for structural idealizations as beams and plates while accounting for transverse shear deformation. Also, their PD dispersion relations are presented and compared with those of classical theory

A novel finite element technique for moisture diffusion modeling using ANSYS

This study presents a novel modeling approach for wetness and moisture concentration in the presence of time dependent saturated moisture concentration by employing the traditional ANSYS thermal and surface effect elements. The accuracy of the present approach is established by comparison with those of the existing ANSYS "diffusion" and "coupled field" elements as well as peridynamic theory. The comparison concerns the desorption process in a fully saturated bar made of two different materials with equal and unequal values of solubility activation energy in the presence of time dependent saturated moisture concentration under uniform and nonuniform temperature conditions. The results from the present approach agree well with those of peridynamics and ANSYS "coupled field" elements if the diffusivity is specified as time dependent. Significant deviation occurs if the diffusivity is specified as temperature dependent. The ANSYS "diffusion" element is applicable only for uniform temperature, and deviation becomes significant especially for unequal values of solubility activation energy

A lightweight approach for airborne wind turbine drivetrains

Buoyant airborne wind turbines are devices capable of harnessing stronger winds at higher altitudes and with their automated and rapidly deployable system they are suited to niche applications such as emergency power generation. Although much of the wind turbine technology for these systems is common with their ‘grounded’ cousins, an additional design limitation is the requirement for the wind turbine equipment to be lightweight. This paper concentrates on the drivetrain of the wind turbine and the different potential ways of reducing its mass. A buoyant airborne wind turbine with different types of drivetrains, going from gearless to geared systems with distinct gear ratios, has been analysed. Special attention was paid to the mass of the supporting structure of the permanent magnet electrical generator and this was minimized by utilising low density materials, such as composites, in its design. The model showed that a significant reduction in the mass of the drivetrain can be achieved in the gearless case by using materials with a higher ratio of Young’s Modulus to density for the electrical machine supporting structure. For the geared systems, mass decrease was less significant as the gearbox mass had also to be considered. Keywords: Airborne, lightweight, generator structure, composite material

Moisture diffusion modelling by using peridynamics

The moisture concentration in electronic packages can be determined based on the “wetness” approach. The wetness parameter representing the ratio of the moisture concentration with respect to the saturated concentration value of the material is continuous along dissimilar material interfaces. If the saturated concentration value is not dependent on temperature or time, the wetness equation is analogous to the standard diffusion equation whose solution can be constructed by using any commercial finite element analysis software. However, the time dependency of saturated concentration requires special treatment under temperature dependent environmental conditions such as reflow process. The saturated concentration values of most polymer materials in electronic packages are mostly dependent on temperature. As a result, the wetness equation is not directly analogous to the standard diffusion equation. This study presents peridynamic solution of the wetness equation with time dependent saturated concentration. The approach is computationally efficient as well as easy to implement without any iterations in each time step. The implementation is achieved by using the traditional elements and solvers available in a commercial finite element software

Crack growth modeling and simulation of a peridynamic fatigue model based on numerical and analytical solution approaches

Fatigue crack growth assessment of 2024-T3 aluminum alloy is carried out on the basis of a recently developed peridynamic fatigue model. The governing remaining-life equation of the peridynamic fatigue model has been solved by two different approaches i.e. numerical and analytical approaches to perform fatigue-crack growth simulations for 2024-T3 aluminum specimen with a pre-existing crack. Remaining-life parameters of the numerical and analytical solution approaches are determined by calibrating with the experimental crack growth data. Fatigue crack growth predictions, and associated material deformation of the specimen under various loading conditions are simulated by the two approaches. Predicted results show that the numerical approach has shortcomings in accurate predictions of crack growth rates for the application of different loading conditions, while the analytical approach can be applied for a wide range of loading conditions with good prediction accuracy and stable simulations of the material deformation with a growing crack. Furthermore, it is found that the computational time of the analytical approach is considerably shorter in comparison with the numerical approach

Different Bayesian methods for updating the fatigue crack size distribution in a tubular joint

Offshore platforms are prone to fatigue damage. To evaluate the fatigue damage, these platforms are periodically inspected during the in-service lifetime. Inspection activities provide additional information, which includes detection and measurement of crack size. A Bayesian framework can be used to update the probability distribution of the uncertain parameters such as crack size. After updating the distribution of the crack size, it is possible to improve the estimation of joint reliability. The main purpose of this study is to present different methods of Bayesian inference to update the probability distribution of the crack size using the inspection results and to demonstrate how the results are different. Two different methods are presented; analytical (conjugate) and numerical methods. The advantages and shortcomings of each method are discussed. To compare the results of the analytical and numerical methods, two different situations are considered; updating the crack size distribution for a particular joint and updating the crack size distribution for several joints that have almost the same conditions. Although the proposed methodology can be applied to different kinds of structures, an example of tubular joints in a specific jacket platform is presented to demonstrate the proposed approach and to compare the results of two methods

Microstructural investigation of plasma sprayed ceramic coatings using peridynamics

The present study deploys a continuum mechanics approach called peridynamics to investigate the damage behaviour of a 2D microstructure, which was taken from a plasma sprayed ceramic coating used in solid oxide fuel cell (SOFC) sealing systems. At the beginning, two benchmark cases, namely, plate with a hole as well as plate with a single edge notch, are considered. The results are compared to an analytical solution and a very good agreement is obtained. Based on these findings, a microstructural model from a plasma sprayed ceramic coating of SOFC sealing systems is investigated. These micromechanical simulations show that structural defects influence the crack initiation as well as the crack propagation during interconnecting the defects. Typical crack mechanisms, such as crack deflection, crack shielding or multiple cracking, are observed. Additionally, an anisotropy of the effective mechanical properties is observed in this heterogeneous material, which is well known for plasma sprayed materials

Peridynamic wetness approach for moisture concentration analysis in electronic packages

Within the finite element framework, a commonly accepted indirect approach employs the concept of normalized concentration to compute moisture concentration. It is referred to as “wetness” approach. If the saturated concentration value is not dependent on temperature or time, the wetness equation is analogous to the standard diffusion equation whose solution can be constructed by using any commercial finite element analysis software such as ANSYS. However, the time dependency of saturated concentration requires special treatment under temperature dependent environmental conditions such as reflow process. As a result, the wetness equation is not directly analogous to the standard diffusion equation. This study presents the peridynamic wetness modeling for time dependent saturated concentration for computation of moisture concentration in electronic packages. It is computationally efficient as well as easy to implement without any iterations in each time step. Numerical results concerning the one-dimensional analysis illustrate the accuracy of this approach. Moisture concentration calculation in a three-dimensional electronic package configuration with many different material layers demonstrates its robustness

System reliability calculation of jacket platforms including fatigue and extreme wave loading

Jacket platforms are redundant structures. Therefore, reliability analysis at system level is more applicable than at component level. Conventionally, system reliability analysis is estimated based on either fatigue loading or extreme environmental loading. The purpose of this study is to perform the structural reliability analysis of a jacket platform under both fatigue and extreme loading. In this study the fatigue limit state is defined based on the crack size, which is obtained by a fracture mechanics approach. The probability of failure for each component is calculated by using Monte-Carlo simulation. Important failure paths are identified by using a searching process. The system failure criterion is evaluated by comparing the platform strength and loading distributions in terms of base shear. In order to define a probabilistic formula for load, a global response surface method is adopted to relate the wave height to the response of the structure. A pushover analysis is also carried out to determine the capacity of the platform. Having calculated the structure strength and loading distributions, the annual probability of failure under extreme wave is calculated and compared to the tolerable probability of failure or target reliability. An application of the approach is presented